Protective recirculation means for heat exchangers



` Aug. 3l, 1965 K, G. CRI-:ws ETAL PROTECTIVE REGIRCULATION MEANS FOR HEAT EXCHANGERS Filed April 2l. 1960 INVENTORS.' KENNETH G. CREWS, JOHN L. MASON,

Agenf.

United States Patent O 3,203,475 PROTECTHVE RECERCULATIN MEANS FR HEAT EXCHANGERS ienneth G. Crews, Garden Grove, and John lL. Mason, y

In t-he operation of heat exchangers of the type wherein a first uid at one temperature is cooled by heat transfer to a second fluid at a lower temperature, it is often desirable to provide means whereby the temperature of the inlet fiuid to be cooled may be adjusted to a tolerable or an optimum level before it is admitted to the heat transfer elements themselves. This is especially true in vehicular and similar practice where it is important that the size and weight of component assemblies be minimal and where the materials of construction are often called upon to perform close to the limits of their strength and thermal capabilities.

The present invention, which relates to a novel construction for heat exchangers, such as those commonly used to cool liquid or gaseous ffuids in propulsion, control, heating or refrigeration systems, provides effective means for adjusting the temperature of the inlet fluid to a level consistent with the thermal tolerance and optimum perform-ance of the heat exchange elements themselves. More specifically, it relates to such a construction which is particularly adapted to use with heat exchangers of .the type in which a first fluid, either liquid or gaseous, `is to be cooled by heat transfer, through a thermally conductive flow barrier, to la second fluid, which may likewise be either liquid or gaseous.

One of the objects of the invention is to provide means for protecting the interior structure of a heat exchanger of the type described from the adverse effects of high tem-perature by precooling the inlet fluid admitted thereto.

Another object of the invention is to provide such precooling of the inlet liuid through the introduction and 'admixture therewith of a recirculated portion of iiuid which has been cooled by passage through the heat exchanger.

Another object of the invention is to provide means for metering the quantity of cooled fluid to be admitted to the heat exchanger inlet and fo-r assuring that said fluid will be uniformly dispersed in the inlet fluid so as to effectively lower the temperature thereof.

Another object of the invention is to provide means whereby the quantity -of cooled fluid introduced into the inlet of the heat exchanger may be regulated in accordance with the temperature of the fluid at either the inlet or the outlet thereof, or in accordance wtih other parameters that may be of critical importance in particular applications.

Another object of the invention is to provide means for the introduction of cooling fluid at a heat exchanger inlet so as to form a thermally protective boundary layer to shield the structure at the region of the inlet from l direct contact with high temperature incoming fluid.

Another object of the invention is to provide for the introduction of cooled fluid to a heat exchanger inlet by self-energized means responsive to the .prevailing iiow conditions therein.

Still further objects of the invention will be apparent to those skilled in the art from the following specification and the appended drawings.

The invention may `be more clearly understood by reference to Ithe accompanying drawings, which are intended only to illustrate typical preferred practice thereof, it `being understood that variations in constructional details apparent to those skilled in the art may be made ICC without departing from the spirt or scope of the invention. In the drawings, in which like elements are designated by like reference numerals:

FIG. l is a partially schematic View of Va heat exchanger Iaccording to the present invention;

FIG. 2 is a sectional View, taken perpendicular to the plane of FIG. l and along the line 2-2 thereof, further illustrating the construction of the core in which heat transfer is effected;

FIG. 3 is a sectional view illustrating an alternate con-l struction for certain elements of the heat exchanger shown in FIG. l; -and FIG. 4 diagrammatically illustrates an embodiment of the invention in which the recirculation of cooled fluid is controlled -in accordance with a measurable parameter.

Referring now to lFlG. l, a heat exchanger of the general type described is schematically illustrated in cross section. A fluid inlet 1 communicates, through a diffuser or manifold 11, with a plurality of tubular elements 2 which may, in certain practices of the invention, be arranged in separate groups so as to achieve a compact land thermally efficient structure. In the embodiment shown, lfor example, the tubular elements 2 secured between header plates 12 and 13 are grouped in a first pass 3, wherein the fluid to be cooled iiows from bott-om to top as shown in the drawing, and a second pass 4, wherein the fluid flows in the reverse direction, communication between the first and second passes being lprovided by a transfer passage 14, which may, for example, be formed by a suitably shaped cover 5 secured to the top header plate `12, the space between the cover '5 and the header plate 12 being sufficient to afford unimpeded flow communie-ation lbetween the first and second passes `3 and 4. From the second pass 4, the fluid is conducted through a suitably shaped collector 15 to an `outlet 21.

lA fluid coolant is conducted, via a conduit 22, around the exterior surfaces of the tubular conduits 2 comprising the first and second passes 3 and 4, the header plates 12 and 13 and the side wall-s of the conduit 22 serving to define a fluid-tight enclosure therefor. As will be apparent to those skilled in the art, the liow of coolant through the conduit 22 should preferably be from left to right as shown in the drawing; that is, the coolant should traverse the second pass 4 before traversing the first pass 3, maximal heat transfer being effected when the temperature difference between the two fluids is greatest.

As previously discussed, it frequently occurs that heat exchangers of the type shown must be used at or near the maximum temperature at whic-h the materials of their construction may be safely or eiiiciently used. Where this .is the case, it is desirable to provide some means for regulating the temperature of the uid introduced at the inlet 1, thereby to assure eiiicient and safe operation. It will be apparent, however, that many cases may occur, for example, in the cooling of gas turbine exhaust gases, Where it is not feasible to accomplish such regulation without either altering the operating parameters of the engine or providing a second, supplementary heat exchanger. To circumvent this diiculy and thereby accomplish a primary object of the invention, namely to afford control of inlet temperature through the recirculation of cooled fluid, the present invention provides a Venturi injector or aspirator 23 positioned in the inlet 1 so as to induce flow thereinto from the outlet 21 through a recirculation passage 24 conected to the throat of the Venturi. Thus, the temperature of the outlet fluid having been lowered by pasage through the first and second passes of heat exchange conduits 3 and 4, its admixture to the inlet uid results in a corresponding reduction in the tempertature thereof. The extent of this reduction is proportional to the temperature difference between the fluid expelled from the outlet 21 after pasage through the exchanger and the uncooled fluid introduced at the inlet 1, and to the relative quantity or mass of cooled fluid introduced via the recirculation pasage 24 and the Venturi injector 23. Accordingly, the present invention provides for the inclusion in the recirculation pasage 24 of appropriate control means in the form of a flow limiter 25. Where the flow and temperature conditions at w-hich the heat exchanger is required to operate are relatively constant, the flow limiter 25 may comprise a fixed metering element or orifice, the maximum rate of flow through which is limited by the establishment of sonic velocity. Where operation over a varying range of conditions is anticipated, however, a variable flow limiter, which may for example be a butterfly, needle, piston or other type of valve,

'controllable in relation to the fluid temperature at the linlet or outlet or to both temperatures, or to other criteria,

may be provided.

FIG. 4 schematically illustrates such an arrangement in which a variable flow limiter or valve 31 is thermostaticaly controlled in response to the temperature of the fluid introduced at the inlet 1. A temperature sensing element 32 is exposed to the inlet fluid so as to develop a signal indicative of the temperature thereof for transmission to a valve actuating means 33. It will be appa-rent to those skilled in the art that the temperature sensing element 32 and the valve actuating means 33 may operate on mechanical or electrical principles or on a combination thereof and may be selected for particular applications and design conditions `from a wide variety of such instruments well known in the art and readily available in commerce. Further, it is to be understood that the invention is not limited to the particular arrangement of sensing and control elements shown, but that numerous variations thereon may be devised to meet particular operating requirements. The sensing element 32, for example, may be moved downstream of the Venturi injector 23 so as to provide, in effect, a feedback loop in the control system, or it may be positioned in the outlet 21 or in the conduit 22. Similarly, a differential sensing instrument responsive to the temperature difference between the inlet and outlet fluid may be used, or alternately, a measurable physical parameter remote from the Aheat exchanger itself may, in some cases,'be used to develop control signals for operation of the variable flow limiter 31.

As previously mentioned, the temperature reduction -of the incoming fluid afforded by the present invention is proportional to the relative mass of fluid introduced at the Venturi injector 23 and the temperature difference between the incoming fluid at the inlet 1 and the fluid expelled at the outlet 21. Thus, for example, if the ytemperature of the incoming fluid is designated T1 and that of the expelled fluid T3, and the mass of fluid recirculated through the conduit 24 and Venturi injector 23 is a fraction x of the mass originally introduced at the inlet 1, the temperature T2 of the mixed fluids leaving the injector 23 may be determined according to the approximate equation:

In conjunction with the physical characteristics of the particular fluid under consideration, this expression affords means for computation of the degree of recirculation required for a specific application.

In cases where it may be more important to protect the structure of the inlet diffuser 11, rather than the interior of the heat exchanger itself, from the effects of high incoming fluid temperatures, an alternate form of Venturi injector 34 as illustrated -in FIG. 3 may be used to advantage. In the construction shown, the Venturi injector 34 is provided with an annular port 35 positioned in the throat of the Venturi and in flow communicating relation with the recirculation passage 24. By virtue of this arrangement a protective boundary layer of cooler fluid from the outlet 21 may be distributed over the divergent surfaces of the Venturi injector 34 and the diffuser 11, thereby insulating these surfaces from direct contact with the high temperature fluid introduced at the inlet 1.

It will be apparent from the foregoing specification that the present invention affords simple, economical and effective means for the regulation of heat exchanger inlet temperatures so as to confer the benefits of operating safety and efficiency under conditions where it is necessary to approach the maximum safe thermal limits of the materials of construction. Further, it provides means adaptable to all types of fluid heat exchangers whereby inlet or outlet temperatures, or the difference between said emperatures, may be subject to continuous regulation without incurring undue penalties in the efficiency, complexity or weight of the heat exchange unit or its connecting ducting.

It is anticipated that those skilled in the art will have opportunity to practice numerous variations on the invention as herein disclosed, and it is intended that all such variations falling Within the spirit and scope of the invention be secured to us by United States Letters Patent.

We claim:

1. In combination: a heat exchanger having first and second fluid passages including portions disposed internally of the exchanger in heat transfer relationship for conveying a first, relatively hot fluid and a second relatively cold fluid, respectively, in heat transfer relation to one another; said first passage having first and second fluid inlets and first and second fluid outlets, said first inlet and said first outlet being adapted for connection to an external fluid circuit; means defining a recirculation passage directly communicating said second outlet to said second inlet through which a portion of said first fluid exhausting from said heat exchanger after having been cooled by said second fluid may recirculate to mix with and cool the relatively hot first fluid entering the heat exchanger from said external fluid circuit through said first inlet; means for inducing flow of said first fluid through said recirculation passage from said second outlet to said second inlet; temperature responsive means disposed in efficient heat transfer relation to said first passage adjacent said first inlet so as to be highly responsive to the temperature of the hot fluid entering the heat exchanger through said rst inlet; and means in said recirculation passage controlled by said temperature responsive means for regulating recircuation flow of said first fluid through said recirculation passage in such manner that said recirculation flow increases in response to increasing temperature of the first fluid entering the heat exchanger and decreases in response to decreasing temperature of the first fluid entering the heat exchanger, thereby to maintain the temperature of the combined first fluid flowing from said first and second inlets to said internal portion of said first passage below a predetermined maximum temperature.

2. In combination: a heat exchanger having first and second fluid passages including portions disposed internally of the exchanger in heat transfer relationship for conveying a first, relatively hot fluid and a second relatively cold fluid, respectively, in heat transfer relation to one another; said first passage having first and second fluid inlets and first and second fluid outlets, said first inlet and said first outlet being adapted for connection to an external fluid circuit; means defining a recirculation passage directly communicating said second outlet to said second inlet through which a portion of said first fluid exhausting from said heat exchanger after having been cooled by said second fluid may recirculate to mix with and cool the relatively hot first fluid entering the heat exchanger from said external fluid circuit through said first inlet; means for inducing flow of said first fluid through said recirculation passage from said second outlet to said second inlet; temperature responsive means disposed in eicient heat transfer relation to said first passage adjacent said rst inlet so as to be highly responsive to the temperature of the hot fluid entering the heat exchanger through said first inlet; and valve means in said recirculation passage controlled by said temperature responsive means for regulating recirculation flow of said rst fluid through said recirculation passage in such manner that said recirculation flow increases in response to increasing temperature of the first fluid entering the heat exchanger and decreases in response to decreasing the temperature of the first fluid entering the heat exchanger, thereby to maintain the temperature of the combined rst fluid flowing from said first and second inlets to said internal portion of said first passage below a predetermined maximum temperature.

3. In combination: a heat exchanger having first and second fluid passages including portions disposed internally of the exchanger in heat transfer relationship for conveying a first, relatively hot fluid and a second relatively cold fluid, respectively, in heat transfer relation to one another; said first passage having first and second fluid inlets and first and second fluid outlets, said rst inlet and said rst outlet being adapted for connection to an external fluid circuit; rneans defining a recirculation passage directly communicating said second outlet to said second inlet through which a portion of said first fluid exhausting from said heat exchanger after having been cooled by said second fluid may recirculate to mix with and cool the relatively hot rst fluid entering the heat exchanger from said external lluid circuit through said first inlet; means for inducing ilow of said first fluid through said recirculation passage from said second outlet to said second inlet; a valve in said recirculation passage; and means including a temperature sensing element situated directly in said rst inlet for operating said valve in such manner that said valve opens to increase fluid ow through said recirculation passage in response to increasing fluid temperature in said first inlet and closes to decrease fluid flow through said latter passage in response to decreasing fluid temperature in said first inlet, thereby to maintain the temperature of the combined first uid flowing from said rst and-'second inlets of said internal portion of said first passage below a predetermined maximum temperature.

References Cited by the Examiner UNITED STATES PATENTS 1,223,976 4/ 17 Hiller 122-412 1,749,654 3/30 Wyndham, et al 165--108 2,104,333 1/ 38 Rosenblad 165-34 2,178,805 11/39 Olcott 165-40 2,363,870 1l/44 Karlsen, et al. 165-7 2,488,267 11/ 49 Cassie.

2,836,399 5/58 Fallon 165-108 3,063,681 11/62 Duguid.

CHARLES SUKALO, Primary Examiner.

HERMAN BERMAN, HERBERT L. MARTIN, PERCY L. PATRCK, Exmm'ners. 

1. IN COMBINATION: A HEAT EXCHANGER HAVING FIRST AND SECOND FLUID PASSAGES INCLUDING PORTIONS DISPOSED INTERNALLY OF THE EXCHANGER IN HEAT TRANSFER RELATIONSHIP FOR CONVEYING A FIRST, RELATIVELY HOT FLUID AND A SECOND RELATIVELY COLD FLUID, RESPECTIVELY, IN HEAT TRANSFER RELATION TO ONE ANOTHER; SAID FIRST PASSAGE HAVING FIRST AND SECOND FLUID INLETS AND FIRST AND SECOND OUTLETS, SAID FIRST INLET AND SAID FIRST OUTLET BEING ADAPTED FOR CONNECTION TO AN EXTERNAL FLUID CIRCUIT; MEANS DEFINING A RECIRCULATION PASSAGE DIRECTLY COMMUNICATING SAID SECOND OUTLET TO SAID SECOND INLET THROUGH WHICH A PORTION OF SAID FIRST FLUID EXHAUSTING FROM SAID HEAT EXCHANGER AFTER HAVING BEEN COOLED BY SAID SECOND FLUID MAY RECIRCULATE TO MIX WITH AND COOL THE RELATIVELY HOT FIRST FLUID ENTERING THE HEAT EXCHANGER FROM SAID EXTERNAL FLUID CIRCUIT THROUGH SAID FIRST INLET; MEANS FOR INDUCING FLOW OF SAID FIRST FLUID THROUGH SAID RECIRCULATION PASSAGE FROM SAID SECOND OUTLET TO SAID SECOND INLET; TEMPERATURE RESPONSIVE MEANS DISPOSED IN EFFICIENT HEAT TRANSFER RELATION TO SAID FIRST PASSAGE ADJACENT SAID FIRST INLET SO AS TO BE HIGHLY RESPONSIVE TO THE TEMPERATURE OF THE HOT FLUID ENTERING THE HEAT EXCHANGER THROUGH SAID FIRST INLET; AND MEANS IN SAID RECIRCULATION PASSAGE CONTROLLED BY SAID TEMPERATURE RESPONSIVE MEANS FOR REGULATING RECIRCULATION FLOW OF SAID FIRST FLUID THROUGH SAID RECIRCULATION PASSAGE IN SUCH MANNER THAT SAID RECIRCULATION FLOW INCREASES IN RESPONSE TO INCREASING TEMPERATURE OF THE FIRST FLUID ENTERING THE HEAT EXCHANGER AND DECREASES IN RESPONSE TO DECREASING TEMPERATURE OF THE FIRST FLUID ENTERING THE HEAT EXCHANGER, THEREBY TO MAINTAIN THE TEMPERATURE OF THE COMBINED FIRST FLUID FLOWING FROM SAID FIRST AND SECOND INLETS TO SAID INTERNAL PORTION OF SAID FIRST PASSAGE BELOW A PREDETERMINED MAXIMUM TEMPERATURE. 